Zero
This feature has a limited use in wireless networks where some clients may overload the network with a number of short packets causing a performance bottleneck. If this is not the case, do not turn it on and leave it zero.

I don't have wirless, but i descoverd this ,
someday I was cheking my clients, and found 1 client doing huge upload speed, it was ~ 60 kb/s
but all his connections (16 connections) are downloading something !!

so I got that he was downloading a file with download manager with 16 connections, and this download for somehow didn't finished , and dropped.

but the download manager insists to send requsts to server, many many fast requests goes on, making the upload speed rased to ~60 kb/s

so I tryed "short packet flood penalty" on that client rule only, and it was amazing the upload speed droped to ~16 kb/s (better than nothing)
i tested many valus tell I found the best ones that lower this upload flooding.

Threshould = 400
padding = 1514 (max allowed)

ANDREW....
if i leave this ON , is there any side effects??? ---- I don't have Wirless on my environment.